Such radial flow compressors have been known, in principle, and special designs of such radial flow compressors have also been proposed for respirators.
WO 87/01599 shows a radial flow compressor, which is driven by pressurized oxygen in order to pump an oxygen-air mixture to the patient. Electrically driven respirators or anesthesia apparatus without pressurized gas supply for intermittent respiration use mostly either reciprocating pumps or continuously operating compressors with valve control. Large-volume reciprocating pumps are unable to follow the spontaneous breathing of patients rapidly enough, and small pistons operated at high frequency generate undesired pulsations in the breathing gas. Continuously operated compressors require an external pneumatic circuit with valves and are therefore technically complicated; in addition, the increase in the temperature of the breathing gas is undesirable. In addition, there are devices which operate as double-flow side-channel compressors based on a special principle of action and permit intermittent forms of exhalation without additional valves based on the manufacture of highly complicated individual parts, and they comprise many components. However, as a consequence of the greatly sloped pressure-flow characteristics of this type of compressor, the necessary properties can be obtained only by means of an expensive control of the characteristics and by the use of a microprocessor.